Diffusion of hydrogen in olivine: Implications for water in the mantle

Journal Article · Tue Apr 10 00:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB04p05079· OSTI ID:5013359

Mackwell, S J ^[1]; Kohlstedt, D L ^[2]

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1. Pennsylvania State Univ., University Park (United States)
2. Cornell Univ., Ithaca, NY (United States)

To investigate the kinetics of diffusion of hydrogen in olivine, single crystals from San Carlos in Arizona have been annealed at temperatures between 800 and 1,000 C under hydrothermal conditions at a confining pressure of 300 MPa. The rate of diffusion is anisotropic, with fastest transport along the (100) axis and slowest along the (010) axis. The fit of the data to an Arrhenius law for diffusion parallel to (100) yields an activation enthalpy of 130 {plus minus} 30 kJ/mol with a preexponential term of (6 {plus minus} 3) {times} 10{sup {minus}5} m{sup 2}/s. For diffusion parallel to (001), as there are insufficient data to calculate the activation enthalpy for diffusion, the authors used the same value as that for diffusion parallel to (100) and determined a preexponential term of (5 {plus minus} 4) {times} 10{sup {minus}6} m{sup 2}/s. The diffusion rate parallel to (010) is about 1 order of magnitude slower than along (001). The measured diffusivities are large enough that the hydrogen content of olivine grains which are millimeters in diameter will adjust to changing environmental conditions in time scales of hours at temperatures as low as 800 C. As xenoliths ascending from the mantle remain at high temperatures (i.e., > 1,000 C) but experience a rapid decrease in pressure, and hence hydrogen fugacity, olivine grains may dehydrate during ascent. By comparison, slow rates of carbon diffusion suggest that carbon will not be lost from olivine during ascent. Thus, low hydrogen contents within olivine and within fluid inclusions in olivine cannot be taken as support for low water contents in the mantle.

• OSTI ID: 5013359
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:B4; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
EARTH MANTLE
MOISTURE
HYDROGEN
DIFFUSION
OLIVINE
PERMEABILITY
ACTIVATION ENERGY
ANISOTROPY
ARIZONA
CRYSTAL STRUCTURE
DEHYDRATION
ENTHALPY
GRAIN SIZE
INFRARED RADIATION
KINETICS
SAMPLE PREPARATION
SPECTROSCOPY
DEVELOPED COUNTRIES
ELECTROMAGNETIC RADIATION
ELEMENTS
ENERGY
FEDERAL REGION IX
MICROSTRUCTURE
MINERALS
NONMETALS
NORTH AMERICA
PHYSICAL PROPERTIES
RADIATIONS
SILICATE MINERALS
SIZE
THERMODYNAMIC PROPERTIES
USA
580000* - Geosciences
400201 - Chemical & Physicochemical Properties